If your budget is as small as it seems, I don't know if your time is best spent putting it towards story. If you look at some of the great games in the past they were great not because they had a really deep story but because they had some really good gameplay mechanics.
It seems like you have a solid idea in the form of a modern stealth/combat RPG. Make most of your uniqueness come from there and ensure that it's locked down air tight, then put extra time and money into the graphics, and then finally get the graphics.
It seems like you have a solid idea in the form of a modern stealth/combat RPG. Make most of your uniqueness come from there and ensure that it's locked down air tight, then put extra time and money into the graphics, and then finally get the graphics.